Traditionally, the diagnosis of upper respiratory tract viral infection was based on clinical history and examination, and did not include laboratory studies, because such studies have a long turn-around time and have little impact on patient management.
Recently, however, antibody-based and nucleic-acid based laboratory studies have significantly shortened the turn-around time of laboratory investigations to the point that clinical management, particularly decisions on quarantining and cohorting patients, can be positively affected. The recent SARS (Severe Acute Respiratory Syndrome) epidemic has heightened the need for a rapid diagnostic method.
The points of entry of most viral upper respiratory illnesses are the eyes, nose and mouth; the virus frequently gains an initial foothold in the nasopharynx and sometimes the conjunctiva or possibly the nasolacrimal system. Subsequent to the infection of susceptible hosts, viral replication takes place in the host's epithelial cells, causing release of more infectious virus particles into the secretions. Often, the infected epithelial cells detach from the epithelial lining, and can be collected for identification of the virus. Viral particles are also shed into the extracellular space by active secretion or excretion or upon death of the virally infected cells. Methods used to detect virus or virally infected cells include viral culture, direct immunofluorescent microscopy, a variety of immunoassays, and nucleic acid-based diagnostic tests.
Whereas the incidence of uterine cervical carcinoma is greatly reduced in countries with effective cervical cytology screening programs, incidence of nasopharyngeal carcinoma is not affected, as there is no available means of non-invasively or minimal-invasively obtaining cells for exfoliative cytological cancer screening.